JPS6356540B2 - - Google Patents

Description

Detailed Description of the Invention The present invention projects an image on a document onto a uniformly charged photoreceptor to form an electrostatic latent image on the photoreceptor, and develops the electrostatic latent image onto recording paper. This invention relates to prevention of background stains on recording paper in a copying device that performs transfer.

In copying machines, the original on the contact glass plate is pressed against the contact glass plate using a presser plate that has a document holding surface with high light reflectivity. Normally, the operator presses the original document with this presser plate. Make a copy. However, when making one or several copies of each of many originals, it is cumbersome to replace the original on the contact glass plate, so copies are made without using a presser plate, that is, without pressing the original with the presser plate. There are things to do.
If the document is thin, transparent, or translucent when the presser plate is not used, the illumination light will be transmitted through the background of the document, and a corresponding background stain will appear on the recording paper.

An object of the present invention is to prevent such skin staining when the presser plate is not used.

In order to achieve the above object, in the present invention,
The opening and closing of the presser plate is detected by electric elements such as micro switches, pressure-sensitive switches, and photo sensors, and an electric signal indicating that the document has high light transparency is obtained by the operator's switching operation or automatic detection by the photo sensor. , when the presser plate is open (position where it does not press the document) and the document is highly transparent, the presser plate is open (position where it does not press the document).
Controls to prevent background staining are performed, such as increasing the developing bias, increasing the light amount of the exposure lamp, and/or lowering the charging voltage. Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

FIG. 1a shows the configuration of one copying apparatus embodying the present invention. In the copying apparatus shown in FIG. The light is guided to the surface of the photoreceptor on the drum 1 by the second mirror SMI, the in-mirror lens IMI, and the third mirror TMI. On the other hand, the photoreceptor is uniformly charged by the main charger 2, and is exposed to the guided light to form an electrostatic latent image. This electrostatic latent image is made visible by depositing charged toner supplied by the developing device 4. On the other hand, copy paper is fed into the cassette by paper feed roller PSR1 or PSR2.
Extracted from CAS1 or CAS2. The taken-out copy paper is sent to the transfer section by rotating the registration rollers 6 in synchronization with the position of the latent image (the edge of the document). In the transfer section, the toner adhering to the latent image area is transferred onto the copy paper by the transfer charger 7, and the copy paper is separated from the drum 1 by the separation roller 8 and transferred to the fixing heater.
The HEP fuses (fixes) the toner onto the copy paper, and the copy paper is sent to the output tray COT.
On the other hand, the toner remaining on the drum 1 is neutralized by a static eliminating charger 5 and collected by a cleaning roller 10. 11 is a cleaning blade.

The document reading scanning system includes illumination light HLA, mirror FMI,
It consists of SMIs and a carriage that moves them so that the optical path length does not change.

The document presser plate BP is rotatable around the shaft 3, and a portion of the lower end of the document presser plate BP is cut out, and a soft leaf spring 12 is fixed thereto as shown in FIG. 1b. A normally open micro switch 13 is installed at a position that is pressed down by the leaf spring 12 when the presser plate BP is open.
When the presser plate BP is open as shown in FIG. 1b, the microswitch 13 is closed. Further, a key switch 14 (FIG. 1d) that is closed by the operator when the document is highly transparent is installed on the keyboard KB.

The developing device 4 is of a wet developing type, as shown in detail in FIG. 1C, and includes a developer supply pump 4a and detection electrodes 291 to 2 for detecting surface potential.
93 and a developing electrode 27. A developing bias circuit of this developing device 4 is shown in FIG. 1d. In this developing bias circuit, the detection electrodes 291 to 29
3 is connected to the anodes of the diodes 32 to 34, and the cathodes of the diodes 32 to 34 are connected to the operational amplifier 35.
Connected to the positive phase input terminal of the Therefore, the smallest output of the detection electrodes 291-293 is selected by the diodes 32-34 and applied to the operational amplifier 35 as the residual potential detection output of the photoreceptor 21. The positive and negative power supply terminals of the operational amplifier 35 are connected to the emitters of an NPN transistor 36 and a PNP transistor 37.
6 is grounded, and the collector of transistor 37 is connected to negative DC power supply 38. Resistors 39, 40 and capacitors 41, 42 are connected in parallel between the collectors and bases of the transistors 36, 37, and constant voltage diodes 43, 44 are connected between the bases of the transistors 36, 37 and the output terminal of the operational amplifier 35. is connected, and the output terminal of the operational amplifier 35 and the negative phase input terminal are connected. Therefore, the output of the DC power supply is supplied to the operational amplifier 35 through the transistors 36 and 37, and the supply voltage is kept constant by the voltage regulator diodes 43 and 44, and the supply voltage level varies depending on the input voltage and has a wide range. Operates over input voltage range. Detection electrode 291
~293 is the operational amplifier 35 via the cable 45
The shield wire of this cable 45 is connected to the output terminal of the operational amplifier 35. This includes the ground capacitance of the detected charge itself, the input capacitance of the operational amplifier 35, the leakage current, and the cable 4
This is to prevent toner from settling on the detection electrode due to the grounding capacitance of the cable 45, and a voltage close to the detection output of the detection electrode is applied to the cable 45, and the cable 45 is grounded in an alternating current manner. The output terminal of the operational amplifier 35 is connected to the normally closed contact 15a of the relay 15 via a resistor 46. The normally closed contact 15a is connected to a negative constant voltage source through a resistor 47, and also connected to a negative constant voltage source through a resistor 48 and 4.
9 to a positive constant voltage source. The connection point between resistors 48 and 49 is normally open contact 1 of relay 15
5b. Coil 15 of relay 15
C is connected to a relay driver (amplifier) 16, and the relay driver 16 energizes the coil 15C when the output of the AND gate 17 is "1", and changes the movable contact piece 15d of the relay 15 to the normally open contact side. close. In this embodiment, since the charge on the surface of the photoreceptor of the drum 1 that is charged by the charger 2 is of positive polarity, when the presser plate BP is open and a document with high light transmittance is being copied, the relay contact 15d is always connected. The open contact 15b is closed to apply a higher developing bias voltage to the developing electrode 27 on the positive side than in normal copying operations, thereby preventing background staining.

Close the presser plate BP, that is, press the document IP with the presser plate BP.
When copying is performed by pressing the key against the contact glass plate, the micro switch 13 is open, so even if the key switch 14 is closed, the output of the AND gate 17 is "0", so the relay 15 is As shown in FIG. 1d, the movable contact piece 15d is in contact with the normally closed contact 15a, and a normal auto bias voltage is applied to the developing electrode 27. In other words, the detection electrodes 291~
293 generates an induced potential corresponding to the surface potential of the photoreceptor, which causes a voltage proportional to the voltage to appear at the output terminal of the operational amplifier 35, which causes the developing electrode 27 to generate an induced potential that is lower than the surface potential of the photoreceptor, that is, only the image area. A voltage is applied that causes the toner to adhere to the surface. As a result, development is performed with less background staining. This type of automatic bias control can be used to
Since it is set for the state where the IP is held down,
If the original IP has high light transmittance with the presser plate BP open, background stains will still occur.

Therefore, when copying a document with high light transparency with the presser plate BP open, press the key switch 1.
Copy with 4 closed. At this time, since the presser plate BP is open, micro switch 1
3 is closed, and the key switch 14 is closed, so the output of the AND gate 17 is "1", the coil driver 16 energizes the relay coil 15C, and the movable contact piece 15d of the relay 15 moves to the normally open contact 15b side. When closed, a voltage obtained by adding a positive bias to the output of the operational amplifier 35 is applied to the developing electrode 27.
This reduces the adhesion of toner to the background portion where the amount of light received is low and the surface potential is high, resulting in copies with less background stains.

Note that an electric element or circuit such as a pressure sensitive switch, a magnetically sensitive switch, or a photo sensor may be used instead of the micro switch 13, and a photo sensor may be used instead of the key switch 14 on a part of the contact glass plate on which the document IP is placed. An automatic detection circuit that detects the light transmittance of the original IP may be used.

When detecting the light transmittance of a document using a photo sensor, for example, as shown in FIG. 19
₁ to 19 ₃ , select the one with the largest detected amount of light among those detection signals, compare it with the standard value, and if the detected value is smaller than the standard value, increase the developing bias. good. Also, presser plate BP
The surfaces facing each of the heads 19 ₁ to 19 ₃ are made of a color having low light reflectivity, such as black. In FIG. 2a, CG is a contact glass plate.

An example of a circuit for automatically detecting the light transmittance of a document using a photo sensor is shown in FIG. 2b. 2nd b
In the figure, 19 ₁ T to 19 ₃ T are phototransistors of reflective photo sensor heads 19 ₁ to 19 ₃ , respectively.
The impedance of 9 ₁ T to 19 ₃ T is low when the amount of light is large, and becomes high when the amount of light is small. The emitter potentials of phototransistors 19 ₁ T to _{19 3} T are determined by comparators (e.g. Schmitt circuits, differential amplifiers).
20 ₁ to 20 ₃ and compared with the reference voltage Vref. Each of the comparators 20 ₁ to 20 ₃ outputs "1" when the amount of light received by each of the phototransistors 19 ₁ T to _{19 3} T is equal to or greater than the amount of background (white) reflected light corresponding to Vref.
If it is less than that, it will produce an output of "0". The reason why three heads are used is that since an image (black) may exist below the head, one of the heads is used to detect the amount of reflected light on the background (white) part. When any of the phototransistors 19 ₁ T to _{19 3} T detects background reflectivity of a predetermined level or higher (that is, when any of the comparators 20 ₁ to 20 ₃ outputs "1"), an AND gate is output via the OR gate 21. 17 is applied. As a result, the AND gate 17 is held off (output "0"), and the coil driver 16 does not energize the coil 15C of the relay 15. However, which phototransistor 1
If the background reflectivity of 9 ₁ T to 19 ₃ T is not detected at a predetermined level or higher, the outputs of all the comparators 20 ₁ to 20 ₃ are "0" and the inverted input of the AND gate 17 is "1".
Then, when the presser plate BP is open (13 is closed), the output of the AND gate 17 is "1" and the coil driver 1 is
6 energizes the coil 15C of the relay 15. As a result, a correction bias corresponding to the open presser plate BP is applied to the developing electrode 27. In this way, by using a photo sensor that automatically detects the light transmittance of the original, the development bias is automatically corrected.

In the embodiments described above, background staining is prevented by controlling the developing bias, but it can also be prevented by lowering the corona discharge voltage of the charger 2 or increasing the voltage and/or current of the exposure lamp HLA. Similarly, skin stains can be prevented. In this case, for example, the voltage applied to them may be changed by switching and connecting the voltage terminals using the relay 15.

As described above, according to the present invention, when a document with high light transmittance is copied without being pressed by a presser plate, staining of the recording background due to transmission of document illumination light can be automatically prevented.

[Brief explanation of drawings]

FIG. 1a is a side view showing the configuration of one type of copying apparatus embodying the present invention, FIG. 1b is an enlarged cross-sectional view of the legs of the document presser plate BP, and FIG. 1C is a diagram showing the configuration of the developing device 4. The cross-sectional view, FIG. 1d, is a circuit diagram showing a developing bias circuit. FIG. 2a is a plan view showing the arrangement of photo sensors in one embodiment of the present invention, and FIG. 2b is a circuit diagram showing a light transmittance detection circuit of an original using these photo sensors. HLA: Light, IP: Original, FMI, SMI,
TMI: Mirror, IMI: In-mirror lens, 1: Drum, 2, 5, 7: Charger, 3: Axis, 4: Developing device, 6: Registration roller, 8: Separation roller,
9: Recording paper transfer line, 10: Cleaning roller, 11: Cleaning blade, 12: Leaf spring, 13: Micro switch, 14: Key switch, 15: Relay, 16: Coil driver, 1
7: AND gate, 18: Original positioning frame, 19
₁ ~ 19 ₃ : Reflective photo sensor head, 19 ₁ T ~
19 ₃ T: Phototransistor, 20 ₁ to 20 ₃ : Comparator, 21: OR gate, 27: Development electrode, 29
1-293: detection electrode.

Claims (1)

[Claims] 1. A first electric signal indicating that the presser plate is not at the original holding position of the detection means for detecting whether or not the holding plate that holds the original on the contact glass plate is at the original holding position, and manual operation or automatic detection. When a switch or an electric circuit indicating that the light transmittance of the document is increased by the second electric signal indicating that the light transmittance of the document is increased is present, the presser plate is in the document holding position. Increasing the developing bias voltage in the direction of the charge polarity of the transfer photoreceptor, increasing the light intensity of the exposure lamp, and
A copying control method that prevents background stains on recording paper by at least one of the following: lowering the charging voltage.